Closed cycle cooler including a cryostat



Sept. 7, 1965 .1.s. BULLER ETAL 3,204,422

CLOSED CYCLE COOLER INCLUDING A CRYOSTAT 9 Sheets-Sheet 1 Filed May 6, 1963 .Nkw

Sept. 7, 1965 J. s. BULLER ETAL 3,204,422

oLosED CYCLE cooLER INCLUDING A cRYosTAT Filed May' e, 1963 9 sheets-sheet 2 Sept. 7, 1965 J. s. BULLER ETAL 3,204,422

CLOSED CYCLE COOLER INCLUDING A CRYOSTAT Filed May 6, 1965 9 Sheets-Sheet 3 EL/zer. 3.

CLOSED CYCLE COOLER INCLUDING A CRYOSTAT Filed May 6, 1963 9 Sheets-Sheet 4 1 GD @00 @J f in GD Sept. 7, 1965 J. s. BULLER- ETAL Filed May 6, 1963 CLOSED CYCLE COOLER INCLUDING A CRYOSTAT 9 Sheets-Sheet 5 Sept. 7, 1965 J. s. BULLER mL 3,204,422

CLOSED CYCLE COOLER INCLUDING A CRYOSTAT Filed May 6, 1965 9 Sheets-Sheet 6 /az j@ @Z r 3 I v Sept. 7, 1965 J. s. BULLER ErAL 3,204,422

CLOSED CYCLE COOLER INCLUDING A CRYOSTAT Filed May 6, 1963 9 Sheets-Sheet 7 Sept. 7, 1965 J. s. BULLER ETAL 3,204,422

CLOSED CYCLE COOLER INCLUDING A CRYOSTAT Filed May 6, 1965 9 Sheets-Sheet 8 Sept 7, 1965 J. s. BULLER ETAL 3,204,422

CLOSED CYCLE COOLER INCLUDING A CRYOSTAT Filed May 6, 1965 9 Sheets-Sheet 9 United States Patent O 3,204,422 CLOSED CYCLE COOLER INCLUDING A CRYOSTAT Joseph S. Buller, Santa Barbara, and Garland K. Guiler,

Goleta, Calif., assignors to Hughes Aircraft Company,

Culver City, Caiif., a corporation of Delaware Filed May 6, 1963, Ser. No. 278,304 8 Claims. (Cl. 62-192) This invention relates generally to cooling systems, and more particularly to closed cycle cooling systems.

Recently a need has developed for small, etiicient, closed cycle coolers for cooling various types of electronic devices. Usually, these applications require av cooling system which is small and which is light-weight and which has a relatively long, useful life.

Systems of this type employ gases as the cooling medium. These gases are compressed and are then subjected to controlled expansion, usually in some type of Joule-Thompson device such as a cryostat wherein gas expansion, cooling and eventual liqueiication takes place.

The nature of a Joule-Thompson device requires that the gas be maintained relatively free of contaminants, otherwise clogging takes place and the practice has been in the past to utilize unlubricated compressors in such closed cycle systems to avoid gas contamination. Such unlubricated compressors present many problems, among which are excessive wear andthe generation of excessive amounts of heat which in a closed cycle system is diflicult to remove.

One object of this invention is to provide an improved closed cycle cooling system which is simple with respect to operational requirements and effective in operation.

Another object of this invention is to provide an improved cooling system which is very highly miniaturized with respect to cooling power requirements.

Another object of this invention is to provide an improved closed cycle cooling system which has a relatively long life.

A further object of this invention is to provide an improved closed cycle cooling system capable of operating over relatively long periods of time without clogging and without contaminating the gas.

Still another object of this invention is to provide an improved closed cycle cooling system which will operate over a relatively long period of time without requiring makeup gas.

Further separate and combined objects of this invention are to provide an improved closed cycle cooling system which is light in weight, which is easily cooled, which is easily maintained and which provides good temperature regulation of the liqueed gas.

The objects aforesaid are accomplished according to one embodiment of this invention in a cooling system employing a lubricated compressor for compressing a gas such as nitrogen. The high pressure output of the lubricated compressor is connected to the input of a centrifugal type of oil separator which receives the nitrogen gas and swirls it so that the heavy oil tends to separate from the gas. This oil separator has a gas outlet that is connected to a filter. The filter is one which filters a variety of sizes of oil particles and other contaminants from the nitrogen gas and may include, by way of example, a molecular sieve material in the form of small pellets contained in a predetermined volume of the lter, together with a suitable glass ber paper for entrapping larger sizes of oil particles and other contaminants. The output of the lter is connected to the input of a capillary or distributed throttle ice type of Joule-Thompson cryostat in which the gas is expanded and cooled through repeated recirculating cycles to eventually form liqueiied gas. The output of the cryostat connects to one inlet of a suitable manifold having a second inlet and having an outlet which is connected to the low pressure input ports of the compressor.

At least the compressor and manifold in this assembly is contained within a hermetically sealed gas filled case. The outlet of the cryostat connects with the inlet to the manifold in a hermetically sealed connection extending through the case. Of course, other elements such as the oil separator may also be included within the case. However, such elements as the lter which require maintenance are more conveniently situated eX- ternally of the case, as is the cryostat in which the liquefied gas is formed.

Temperature control is achieved by means of regulating the pressure on the liquefied gas inthe cryostat. This is accomplished by regulating the gas pressure in the case between predetermined minimum and maximum values. This pressure communicates with the cryostat through the manifold. In one practical embodiment of this invention the internal gas pressure was regulated between a low pressure of about 7 pounds per square inch gauge pressure and a high pressure of 10 pounds per square inch gauge pressure. In an arrangement employing liquid nitrogen gas this results in an average liquid nitrogen temperature of about K. As will be seen from an inspection of a standard liquid nitrogen vapor pressure curve, the slope of the curve in this pressure range is relatively steep permitting the pressure excursion indicated in a very narrow temperature range. The pressure regulation afoesaid is achieved by means of high pressure and low pressure controlled valves, the high pressure valve of which connects a third outlet of the oil separator to a suitable storage tank which is capable of receiving the high pressure output of the compressor, which may be of the order of 1500 pounds per square inch, for example, and resulting in a storage tank pressure, say of the order of about 1000 pounds per square inch for a particular ambient temperature, between the upper and lower pressure ranges of the high pressure valve. `The low pressure valve connects the storage tank with the interior of the case and operates in a pressure range in which the higher operating pressure is below the high operating pressure of the high pressure valve and the low operating pressure which is below the lower operating pressure of the high pressure valve.

The compressor takes gas from the case through the gas inlet in the manifold and consequently in operation tends to reduce the gas pressure in the case. The low pressure valve, when the lower pressure range is reached, operates and replenishes the gas in the case from the storage tank, raising the case pressure. If for any reason gas pressure tends to rise above the upper limit, the high pressure valve discharges the compressor high pressure output into the storage tank. The capacity of the storage tank, in one embodiment of this invention, is suicient to take care of leakage and provides a sump to receive nitrogen gas as the ambient temperature rises, and to return gas to the tank as the ambient temperature falls, al1 in response to pressure. For instance, such a tank may be essentially empty when the ambient temperature reaches 65 F. and may be completely lled with gas at maximum pressure as controlled by the high pressure valve when the ambient temperature is about F.

The aforesaid and other objects and advantages will become apparent from a study of the following specification when considered in conjunction with the accompanying drawings in which:

FIGURE l is a block diagram of a closed cycle cooling system embodying the principles of this invention;

FIG. 2 is an elevational view, fragmentary in section, of one practical embodiment of this invention;

FIG. 3 is a plan View, fragmentary in section, of the arrangement illustrated in FIG. 2;

FIG. 4 is an end view of the arrangement illustrated in FIG. 2 with the motor fan shroud removed;

FIG. 5 is a View of the opposite end of the arrangement in FIG. 2 with the end plate removed to reveal certain interior details;

FIGS. 6 and 7 are detailed views, fragmentarily in section, of a three-stage compressor employed in this invention;

FIG. 8 is a cross-sectional view drawn to an enlarged scale of a cryostat employed in this invention;

FIG. 8.a is an enlarged detail of a portion of the cryostat of FIG. 8;

FIGS. 9, 10 and l1 are, respectively, a longitudinal, a top plan View and an illustration of a detail of an oil separator employed in this invention; and

FIGS. 12 and 13 are, respectively, a longitudinal sectional view and an end view of a lilter employed in this invention.

The closed cycle cooling system is illustrated in block form in FIG. l and comprises a compressor 1 which in this instance is a three-stage compressor in which the low, intermediate and high pressure stages are coupled in cascade by means of intercooling coils generally designated 2. These coils couple the outlet of each lower pressure stage to the inlet of the next higher pressure stage as will be described. The compressor is contained within a casing 3 which is hermetically sealed. The coils 2 extend through suitable littings, not shown in this illustration, externally of the casing into the ambient temperature for cooling purposes. As will be described hereinafter, the compressor 1 is oil lubricated. Its high pressure outlet generally designated 1a is coupled to an input port 4 of an oil separator 5 which has a gas outlet port 6 and an oil and gas outlet port 7. Gas outlet port 6 is coupled through case 3 to an inlet port 8 of a lter 9. Outlet port 10 of the lter 9 is coupled to the inlet port 11 of a cryostat 12 which may be a Joule-Thompson cryostat which is preferably of the capillary tube or distributed throttle type, rather than of the orifice type. An outlet port 13 of the cryostat is coupled through case 3 to an inlet port 14 of a manifold 15. Manifold 15 has an inlet 16 communicating with the interior of the case 3 and has an outlet 17 which is coupled to a low pressure inlet port 18 of the compressor 1.

This completes the gas cooling circuit. The compressor compresses the gas which is coupled to the input port 4 of the oil separator 5. Here the majority of the oil is centrifugally extracted from the gas which is admitted to the oil separator. The remaining oil which is entrapped with the gas leaves the gas outlet port 6 of the oil separator and enters the oil filter 9 at its inlet port 8. As will be described, the oil filter comprises a molecular sieve for removing oil molecules and a fine mesh glass fiber paper for filtering larger oil droplets. The outlet 10 of the lter 9 communicating with the inlet 11 of the cryostat 12 transfers gas to the cryostat. Here the gas expands and cools and in successive recycling eventually liquefies. The liquefied gas is maintained at a temperature of the order of 80 K., for instance. Gas flowing from the cryostat enters manifold where it cornbines with gas which is extracted from the gas illed case 3. By means of controls yet to be described the nitrogen gas pressure in the case 3 is maintained between about 7 to 10 pounds gauge pressure which on the liquel'ied nitrogen vapor pressure curve results in an average temperature of about 80 K. The temperature excursion between the pressure limits indicated is small due to the steep slope of the curve in the indicated pressure range.

Temperature control is achieved by means of regulation of pressure within the case 3. This is accomplished by means of pressure switch controlled solenoid valves HV and LV. The solenoid valve HV is controlled by a high pressure switch HS and the solenoid valve LV is controlled by a low pressure switch LS. The high pressure switch HS may be set to close at about 10 pounds gauge pressure when the internal pressure is increasing and will remain closed as the case pressure drops below l0 pounds until a lower limit of 8 pounds internal case pressure is reached, at which point the switch HS opens. Switch LS may be set to open at 9 pounds gauge pressure as the internal pressure in the case increases and to remain open when the case pressure is dropping below 9 pounds until the internal case pressure reaches about 7 pounds, at which time the switch LS closes. The details of the pressure switches and the solenoid valves are not illustrated since these are conventional, commercially available items. The solenoid valves HV and LV are of the spring loaded, normally closed variety and are opened by energization of their solenoids. Solenoid valve HV has an inlet port connected to the outlet port 7 of the oil separator 5 and has an outlet port connected to a storage tank 20. As will be recalled, the port 7 exhausts both gas and oil from the oil separator 5. When the solenoid valve HV is open this gas and oil is discharged to the storage tank 20. Thus, if the internal pressure in the case goes above a predetermined value, the switch HS is closed and energizes the solenoid valve HV. This discharges the output of the compressor into the storage tank 20. As long as the case pressure is high the low pressure switch LS is open. Consequently, the solenoid valve LV is closed. As the compressor operates gas is drawn from the case 3 and the internal case pressure drops. When it goes below 8 pounds the pressure switch HS opens de-energizing the solenoid valve HV which prevents further discharge of gas into the storage tank 20. In one practical embodiment of this invention the high pressure output of the compressor 1 was about 1500 p.s.i. The storage tank 20 is of such size that tank pressure rises to about 1000 p.s.i. during the cycle just described, at which time the case pressure has dropped approximately to 8 pounds to close the solenoid valve HV.

The discharge of gas into the storage tank is of suffi- -cient volume that the gas pressure in the case tends to fall below 8 pounds with continued compressor operation. Assuming for the moment that high pressure switch HS is directly connected to the solenoid valve HV, rather than through an intermittent asher switch FS, as shown, according to one embodiment of this invention, the case pressure tends to continue on down as the compressor operates and eventually drops below 7 pounds. At this point the pressure switch LV operates closing its contacts (not shown) and energizing the solenoid valve LV. When solenoid valve LV opens, the storage tank outlet communicates with the interior of the case 3 resulting in a momentary buildup of internal case pressure which drives the internal pressure up above 9 pounds, at which point the low pressure switch LV opens de-energizing the solenoid valve LS. Continuing operation of the compressor again pulls the gas pressure down below 7 pounds and the cycle is repeated. This cyclic operation of the low pressure switch in the solenoid valve circuit continues until the case pressure is again built up to an average somewhere between 9 and l0 pounds.

Operation of this type is permissible in many applications. For instance, where the cryostat is used to cool an electronic device the rate at which heat energy which must be removed for cooling the electronic device during its normal operation can be computed and the volume of liqueed gas required for this cooling operation can therefore be determined. Thus, it is only necessary to maintain a predetermined minimum volume of liqueied gas in the cryostat in order to effect the required cooling. Thus, the cycle of operation of the pressure control may be such as to maintain at least a predetermined minimum volume of liqueiied gas in the cryostat. This is the simpler form of the control.

The addition of a flasher switch FS or other suitable intermittent type of electric switch, according to a second embodiment of this invention, provides a slightly different type of control which minimizes the pressure excursion within the case 3 and thus tends to maintain a more uniform volume of liquefied gas at the cryostat. By connecting the flasher switch FS in series in the circuit controlling the solenoid valve HV the energization of the solenoid valve HV becomes intermittent. As long as the high pressure switch HS is closed the flasher switch FS operates at its normal rate. The storage tank 20 may now provide any predetermined storage volume above the minimum which is required. The solenoid valve being intermittently operated is effective to intermittently discharge the output of the compressor into the storage tank 20. Gradually, the internal pressure of the case 3 is lowered until the high pressure switch HS is opened. If for any reason the internal pressure of the case 3 goes suiiiciently low with this mode of operation, the cycle of control of the solenoid valve LV corrects the situation by introducing gas from the storage tank to the internal volume of the case 3, as before. The number of cycles of operation of the solenoid valve LV is less when the asher switch is used than With the first embodiment, above.

A minimum size for the storage tank may be determined by reference to the ambient temperature environment in which the cooling system is to operate. Thus, for one embodiment of this invention a storage tank was selected having a volume such that the tank Was empty at 65 F. and filled at about 165 F. This minimum volume may be exceeded if space permits.

As will be seen by inspection of the arrangement illustrated, the outlet port 13 of the cryostat 12 communicates with the internal pressure of the case 3 through the manifold 15 and to case inlet port 16 communicating with the interior volume of the case. Thus, the pressure which is maintained on the liquefied gas in the cryostat is determined by the case pressure. This in turn determines the boiling point of the liquefied gas. For the case of liqueiied nitrogen as described hereinabove pressure excursions in the pressure range of 7 t0 l0 pounds result in an average liquefied nitrogen temperature of about 80 K.

While this description has been made in connection with liquefied nitrogen, it will be appreciated that other gases exhibiting cooling upon expansion may be employed in closed cycle coolers of the type herein described.

The compressor is protected by a relief valve RV connected to the outlet port 7 of the oil separator and set to operate in one embodiment at about 2000 p.s.i. In addition to dumping excess compressor pressure this connection also dumps oil from the oil separator.

Detail assembly FIGS. 2 through 5 are differing assembly views, approximately full size, of one practical embodiment of this invention. As illustrated in these views, the case 3 comprises a generally cylindrical section 3a, a front plate 3b and a back plate 3c. To minimize weight this entire case may be formed of aluminum. The back plate 3c ts neatly within the cylindrical shell 3a and is welded or soldered therein in order to provide a hermetic seal. The front plate 3b is removable. To this end the front end of the outer shell 3a mounts a ring 3c which is welded or soldered to the shell. Ring 3c is provided with a plurality of lugs 3d with threaded holes receiving bolts 3e securing corresponding lugs 3f on the front plate 3b against the lugs 3d. A hermetic seal is achieved between the confronting faces of the front plate 3b and the ring 3c by means of an `2 and 4).

O ring 3g tted within a circular recess in the back face of the front plate 3b in a position where it is squeezed against the confronting face of the ring 3c.

Compressor 1 which is mounted inside the case 3 is driven by means of an induction motor M. Such an induction motor may be operated on 208 volt, 3 phase 400 cycle power or any other suitable power supply. In the embodiment of the invention being described the 400 cycle power supply was employed and the motor operated at about 75% cciency at an operating speed of 11,500 r.p.m. As illustrated in FIG. 2, for instance, the motor M is mounted in a suitable housing 25 which is circular in cross-section and terminates in a flanged end 26 having a lug 27 which indexes in a suitable recess in the inner face of the back plate 3c. If the motor housing is made of brass or aluminum good heat conduction into the back plate 3c is provided to dissipate heat which is generated during operation. The front end of the housing of motor M mounts a gear box generally designated G. This gear box comprises a plurality of gears in a gear train including a gear 28 which meshes with and is driven by a motor pinion 29. Gear 28 is mounted on a crankshaft 30 of the 'compressor and rotates this crankshaft, as will be described. Lubrication for the compressor and gear box is provided by means of a pump P which is mounted in the lower end of the gear box. The pump P includes a piston 32 which is spring loaded against a gear driven cam 33 driven from a motor operated pinion 34. As will be seen from FIG. 2, cam 33 is eccentric with respect to its axis of rotation, thus displacing the piston in its cylinder with each cycle of rotation and pumping oil from the sump S through an oil line 35 into the top of the crank case of the compressor 1 to lubricate the compressor. A tube 35a connects the crank case to the gear box.

As will be described hereinafter the compressor 1 is a three-stage compressor comprising two low pressure stage sections LPSI and LPSZ forming the low pressure stage LPS, an intermediate pressure stage IPS and a high pressure stage HPS as seen in FIG. 3. The output of both sections of the low pressure stage compressor LPS is coupled to the input of the intermediate pressure stage compressor IPS and the output of the intermediate pressure stage compressor IPS is coupled to the input of the high pressure stage compressor HPS. More in particular and with particular reference to FIGS. 3 and 4, each of the low pressure sections LPSI and LPSZ of the low pressure stage LPS are provided with outlet ports 37 and 33 which are connected to a single fluid conductor 39 terminating in a fitting 40 tted to the back face of the front plate 3b and communicating therethrough via a hole, not shown, with a iitting 41 on the front face of the front plate 3b. Fitting 41 is connected to a coil 2a which is external of the case 3 and exposed to ambient temperature for cooling purposes, as described in connection with coil 2 of FIG. l. Coil 2a connects to a fitting 43 on the front face of the front plate 3b communicating through a hole in the front plate with a fitting 44 on the back face of the front plate. Fluid conductor 45 connects itting 44 with an inlet port 46 of the intermediate pressure stage compressor IPS. An outlet port 47 of this intermediate pressure stage is connected by a tube 48 with a fitting 49 on the back face of the front plate 3b and communicates via a hole in the front plate with a fitting 50 on the front face of the front plate. Fitting S0 connects with a coil 2b, the other end of which connects with a tting 51 communicating with a fitting 52 inside the case 3 and which in turn is connected by a tubular conductor 53 with an inlet port 54 of the high pressure stage HPS of the compressor. The outlet port 1a of the high pressure stage of the compressor is connected by a tube 55 to the inlet port 4 of the oil separator 5. Gas is extracted from the oil separator at outlet port 6 and connected by a fluid conductor 6a and ttings 57 and 58 (FIGS. 2 and 3) across the front plate 3b to a iiuid conductor 6b (FIGS. Fluid conductor 6b, as will be seen from '7 FIG. 4 is connected to inlet port 8 of the tilter system. The filter system 9, as illustrated in FIG. 4, is a two-stage filter comprising a iirst stage 9a and a second smaller stage 9b. An outlet port 10a of the filter section 9a is connected to a fluid conductor 10b which is connected to an inlet port 8b of the second stage lilter 9b. Outlet port llt) of the second stage filter 9b is connected by a uid conductor 10c to the inlet port of the cryostat 12 which is not shown in these figures but which is detailed at a later point. The outlet of the cryostat is coupled to a connector 14a as seen in F IG. 3, constituting the manifold inlet 14, which couples into the right end, as viewed, of the manifold 15. Manifold 15 comprises a section 15a coupled at its right end, as viewed, by a suitable fitting 15b, to the back face of the front plate 3b and communicates with a fitting 14. via a hole, not shown, through the front plate. The left end of manifold section 15a communicates with a second manifold section 15o disposed at right angles to the first and the second section terminates in a T section 15d which is open at both ends and provides manifold communication with the interior pressure of the case 3. As will be seen by reference to FIGS. 2 and 5 manifold 15 has its outlet ports 17a and 17b (port 17 FIG. 1) coupled by manifold sections 15e and 151C, respectively, to respective inlet ports 18a and 181; of the low pressure stage of the compressor.

As described in connection with FIG. l, pressure control is achieved by means of the solenoid operated high pressure and low pressure valves HV and LV respectively, and the relief valve RV. These valves are mounted on an upwardly turned end 60 of a bracket 61 which as seen in FIG. 2 extends across the top of the crank case of the compressor 1 and has an upwardly turned front portion 62 which is secured to the front plate 3b. The upwardly turned portion 62 is placed in heat contact with the front end plate 3b and thus provides a means for conducting heat to the front plate to be radiated to the atmosphere from the interior portion of the case. As will be seen by reference to FIG. 3, the oil outlet port of the oil separator 5 is connected by means of a fluid conductor 7a to the inlet port 62 of relief valve RV. The outlet port 63 of the relief valve RV is vented directly to the interior of case 3 to thus vent excessive pressure which vmay be built up in the compressor loop, a branch line of the iiuid conductor 7a is connected to the inlet port 64 of the high pressure valve HV. The outlet port 65 of which is connected by a fluid conductor 65a to the inlet 66 of the storage tank or reservoir 20 (see FIG. 5). The outlet port 6'7 of the storage tank 20 is connected by a liuid conductor 67a to the inlet port 68 of the low pressure valve LV. This is best seen in FIG. 5. The outlet port 69 of the low pressure valve LV is connected to a fluid conductor 69a which opens directly to the interior of the case 3. As will be seen by reference to FIG. 2, the case 3 is surrounded by an outer shell 70 which is spaced therefrom by means of a corrugated sheet 72 which is disposed between the inner shell 3a and the outer shell 70 and which also seats on and is secured to the lugs 3d. The corrugations extend longitudinally of the assembly and make good thermal contact with the inner and outer shells. The front view of the front plate is best seen in FIG. 4. The front plate is provided with fins 73 to enhance cooling. The diameter of the plate is roughly the diameter of the inner shell 3a and as described has lugs 3f for securing the front plate and providing the hermetic seal described.

The front plate and the equipment mounted thereon, including the cooling coils 2a and 2b are enclosed by means of a shroud 75, as seen in FIGS. 2 and 3. The shroud 75 has a central opening therein about which a fan housing 76 is mounted. Fan 77 mounted in the housing 76 on the shaft of a fan motor 78 supported in the shroud, draws air into the fan housing which is moved through the shroud 75 and through the space between the inner and outer shells 3a and 7 0 of the compressor case assembly along the corrugated sections separating the inner and outer shells, thus forced air cooling of the exposed metal surfaces is provided for the compressor case.

An outlet port Sa, which extends from the bottom of the filter stage 9a and is essentially an extension of the outlet pressure line from port 6 of the oil separator may be coupled to a high pressure gauge such as that described and as seen in FIG. 2. Such a gauge for the instant application has a range of from 0 to about 2000 pounds pressure thus indicating the compressor pressure. A low pressure gauge 81 capable of reading pressure over the range of O to 100 pounds per square inch may be coupled directly to the interior of case 3 to read the pressure therein.

Compressor The details of the compressor are illustrated in FIGS. 6 and 7. Here the low pressure stages and the intermediate and high pressure stages are illustrated in greater detail approximately twice actual size. FIG. 6 shows a top view of the compressor assembly with a fragmentary section through a portion of the crank case and the crank shaft while FIG. 7 is a longitudinal cross-sectional View taken through the low pressure and intermediate stages of the compressor. As will be seen by reference to FIG. 7 each compressor section comprises a scotch yoke. The scotch yokes are designated 82 and 83 respectively. The opposite sides of the scotch yoke 82 are connected to the low pressure stage piston 84 and the intermediate pressure stage piston 85. Typical longitudinal sections through the cylinders of the low and intermediate compressor stages appear in FIG. 7. Here the low pressure stage piston 34 strokes in cylinder 90 and the interlmediate pressure stage piston 85 strokes in a cylinder 91. Fluid is admitted to the cylinder through respective ports 18a and 46 on the sides of the cylinders. These are the inlet ports. Valves are eliminated because the pistons control the inlet ports, opening the ports at the bottom ,of the stroke and closing the ports as the piston moves up. Outlet ports 38 and 47 are formed in respective cylinder heads 96 and 97 which close the ends of the low pressure and intermediate cylinders as indicated. Spring loaded outlet valve plates 98 and 99 seat on seats formed on the end faces of the respective cylinders 9i) and 91 and are spring loaded in seated or closed position by respective compression springs disposed between the valve plates and the cylinder heads, as indicated. The ends of the respective pistons are flat, thus as a piston strokes towards the end of a cylinder, as will be seen by reference to piston 85 of the intermediate stage, the piston just makes contact with valve plate 99. This contact is cushioned by an air film which separates the two surfaces. The valve plate 99 opens in the amout necessary against the spring pressure to vent the cylinder while maintaining the pressure for that particular stage of the compressor. The cross-sectional area of the piston chambers and the force provided by the compression spring loading the valve plates, determines the outlet pressure for a particular stage. Each of the scotch yokes is driven by a separate throw on the compressor crankshaft 30, the crankshaft throws mount ball bearing assemblies 102 and 103 as seen in FIG. 6, the outer races of which contact the confronting faces of the respective scotch yokes 82 and 83, thus minimizing friction. As will be seen by reference to FIG. 2, oil is admitted to the crankcase of the compressor through a hole adjacent the upper edge of the crankcase. This hole is designated 104 in FIGS. 6 and 7 and receives tube 35 (see FIG. 2).

Although two low pressure stages have been illustrated herein, this has been done in the interest of simplicity, it being convenient to utilize opposing pistons and cylinders in the assembly. It will be appreciated, however, that the volume of the low pressure stage for the purpose indicated may be increased by utilizing a single low pressure stage having a larger cross sectional area to provide the necessary displacement with each stroke. As will be seen by reference to FIG. 3, the outlet ports 9, 37 and 38 are' coupled into a `single tube-39, in turn coupled via coil 2a to inlet port 46 `of the intermediate pressure stage.

Since the crankcase of the compressor contains oil, lubrication for the bearings in the crankcase and for the pistons results from splashing of the crank arms through the oil sump and movement of the scotch yokes through the oil sump.

Cryostat The cryostat illustrated in FIG. 8 and as discussed in connection with FIG. l, is 'a Joule-Thompson capillary or distributed throttle type of cryostat. The` inlet port 11 of the cryostat communicates with a capillary tube 93 having small internal diameter andhaving edge wound thereabout, as seen in FIG. 8a, a spiral tin 93a for cooling purposes. The finned capillary tubing assembly is then spirally wound about a tubular mandrel 95 which is plugged by means of a plug 95a at its right end, as viewed, on which the finned capillary tubing terminates. The iinned capillary tube is enclosed in a tubular shroud 97 having end plugs 97a and 97b as shown. The plug 97b also seals the left end of mandrel 95. A plug 95C plugs the left side of the mandrel 95 inwardly from its left end as viewed. As will be seen by referenceto FIG. 8a a thread 95e of a suitable insulating material is is spirally wound about the mandrel 95 in a position intermediate the spiral turns of the iinned tubing tendin-g to seal the openingsbetween the tins and the surface` of the mandrel 95 as shown. Similarly another thread 95e of insulating material is disposed between the spiral turns of the tins and the inner surface 'of the shroud 97 tending to seal these edges. A hole 95d is provided in the mandrel 95 to the left of the plug 95h. Outlet port 13, here represented in a tube, communicates with the inner volume of the left end of the mandrel 95 and thus vents this end as shown. The gas which passes through the finned capillary tubing assembly exhausts at the right end of the cryostat and is then forced by the threads to iow in maximum contact with the iins between the tins of the turns 'of the inned capillary tubing as it iiows back to the left end ofthe cryostat assembly where Vit passes through a hole 95C and vents into the outlet port 13. Thus, high eiciency cooling f the finned capillary tube is achieved by passing the cooled gases exhausted from the iinned capillary tubing back over the irlned capillary tubing to an outlet port adjacent the inlet end of the assembly.

Oil separator As described in connection with FIG. 1, the oil separator is a centrifugal type of device'. The details of the assembly are illustrated in FIGS. 9, `and ll showing a longitudinal cross sectional view, a top plan view and a detail respectively of the oil separator. separator comprises a casing 105 which is fitted with a tubular section 106 extending through and sealed in a suitable hole in its upper'end, as viewed. The bottom end of the tubular section terminates adjacent to and above a pedestal supported plate 107 having slotted, upwardly extending flange sections 108. Oil normally drains from plate 108 through the slots. The bottom end of the pedestal supporting the plate 107 is integral with a plate 109 which seals the end of the housing 105. The outlet port 7 through which oil is drained, communicates with the interior of the housing 105 as shown. The upper end of the tubular section 106 terminates in a reduced diameter gas outlet 6 and the inlet port is formed by an extension 4a extending-laterally from the upper end of the tubular section 106. The inlet port 4 extends through the lateral extension 4a into the interior 'of the tubular section 106. As will be seen by reference to FIG. 10, the inlet port 4 enters tangentially with respect to the inner cross section of` the tubular section 106. Thus, gas which enters through the port 4 This oil 1 stituting the outlet port.

swirls within the tube 106. In the process, the heavier oil is centrifugally separated from the gas and tends to impinge on the interior surface of tube 76 collecting in droplets and draining down the wall to drop upon the plate 107. The gas outlet port 6 includes a tube 110 which extends down the inside of tube 106. The pro- Vision of the plate 107 with the upwardly directed ange sections 108 and the provision of the tube 110 substantially prevents oil in liquid state from draining into the gas outlet port 6 should the oil separator be inverted. As will be seen, in the inverted position, oil will tend to cling to the sections 108 of the plate 107 and drop free of the tube 106 rather than into it. Likewise oil on the inner wall of the tube 106 will accumulate about the tube 110 but will not drain into the outlet port 6.

Filter The filter illustrated in FIGS. 12 and 13 is the ilter 9a, as best seen in FIG. 4, and typically represents also the filter 9b which is simply4 smaller in size. Filter 9a comprises a cylinder housing of any suitable material such as brass which is capable of withstanding the output pressure of the compressor. The outlet end of the filter is provided with a small threaded opening 116 to threadly receive the itting 10a, as seen in- FIG. 4, con- The opposite end of the housing 115 is slightly enlarged and is internally threaded to receive the plug 117 provided with transverse holes 118 and 119, in end to end relation, of which hole 119 is in the smaller of the two, and respectively constituting pressure inlet and pressure outlet ports. Hole 119 Connects with a suitable fitting, as seen in FIG. 4, constituting an outlet port 8a which is connected to a suitable pressure gauge to indicate the compressor pressure. A spring loaded pressure plate 120 is disposed in the left end of the filter, as seen in FIG. l2, and has disposed thereagainst a plurality of glass iber iilter papers such as Gelman glass iiber filters, type E. A molecular sieve material is used to ll about half of the inner volume of the filter. This molecular sieve material is of a character which will entrap and hold oil molecules and is in pellet form, formed roughly in the shape of very small cylinders of the order of about l/32 of an inch or less in diameter and about to 1/8 of an inch in length. The remainder of the volume is iilled with the glass ber iilter papers described. The iilter papers seat against a washer 121 which is seated against a plug 117 threaded into the internally threaded end of the ilter housing 115. The oil that is carried by the gas applied to the inlet port 8 of the lter is in part in the form of an oil smoke or vapor containing variations of particle sizes. The very small particles of the oil molecules, roughly of molecular size for instance, pass through the glass iber iilter and are entrapped in the molecular sieve. The larger particles or droplets tend to wet the surface of the glass fiber filter and thus become entrapped in the ilter. Some portion of the larger particles may tend to get through this glass fiber iilter stage and into the molecular sieve. Here these particles, which are too large to be entrapped by the material of the molecule sieve tend to pass through the interstices of the molecular sieve. The residual passing through the sieve then encounters the glass iiber ilters at its other end adjacent the outlet stage, there tending to remove more of the larger heavier oil particles. The glass iiber lters adjacent the outlet stage also tend to seal this end to retain the molecular sieve material and prevent it from entering the outlet port.

The cooling system of this invention is a small ecient unit. One embodiment of this invention weighs nine pounds, is six inches in outer diameter and about nine inches long, requiring about a 200 Watt maximum electrical input to the cooling system. The compressor is very compact. Two inch diameter cylinders make up the rst stage. These are horizontally opposed by the intermediate (1A in. dia.) and high (ls in. dia.) pressure stage cylinders. The inlets through side ports to each cylinder allows a variable effective stroke to achieve a 4.0611 compression ratio for each stage with a 0.380 in. piston stroke. The side port inlet increases compressor reliability by its simplicity and obviates the possibility of a leaky intake valve. On the compression stroke the piston rises fiush with the outlet valve, thus accomplishing an effective zero clearance volume, and resultant high volumetric efficiency. Between stage intercooling and low compression ratios keep gas temperatures down and allow a reasonably close approach to the ideal isothermal compression. The compressor measures 2 x 2 x 41/2 inches over-all and weighs one pound.

The closed cycle cryostat of this invention has been fitted to dewars which have a heat leak of approximately 0.15 watt at 23 C. ambient. It will cool these flasks to 80 K. in a 23 C. ambient with an inlet pressure of 900 p.s.i. and ow rate of 2.2 liters per minute. Operation in 71 C. ambient temperature requires the full compressor output of 3 liters per minute.

At 3000 r.p.m. operating speed, 14.7 p.s.i.a. inlet pressure, 1000 p.s.i.a. outlet pressure, compressor delivery is 3.0 liters per minute with a volumetric efficiency of 87 percent. Total power input is 81.5 watts. Comparison with the computed ideal isothermal power of 24.1 watts yields on overall isothermal eficiency of 29.5 percent. At 23 C. ambient temperature, sustained cryostat operation has been achieved with compressor power inputs as low as 50 watts.

Although but one embodiment of this invention has been herein illustrated and described it will be appreciated to those skilled in the art that numerous variations may be made and the details of the assembly herein described without departure from the sphere and scope of this invention. Accordingly, it is intended that the foregoing disclosure and the showing made in the drawing shall be considered only as illustrative of the principles of this linvention and are not to be construed in a limiting sense.

What is claimed is:

1. A cooling system comprising:

a case;

a compressor mounted in said case and having inlet and outlet ports, said inlet port communicating with the interior volume of said case;

a cryostat externally of said case having an outlet port coupled to the interior volume of said case through said case and having an inlet port;

means having a part extending through said case coupling said inlet port of said cryostat to said oulet port of said compressor;

a storage tank;

means including a rst pressure operated valve means having a pressure sensitive element disposed in said case for coupling said outlet port of said compressor to said storage tank to admit pressure from said compressor to said storage tank when said first pressure operated valve means is opened in response to a predetermined upper limit of case pressure;

and means including a second pressure operated valve means having a pressure sensitive element disposed in said case, for coupling said storage tank to the interior volume of said case to exhaust said Storage tank to said case when said second pressure operated valve means is opened in response to a predetermined lower limit ol case pressure.

2. A cooling system comprising:

a case;

a compressor mounted in said case and having inlet and outlet ports;

a manifold having a discharge port connected to said inlet port of said compressor and having a first inlet port coupled through said case and a second inlet port opening into said case;

a cryostat externally of said case having an outlet port coupled to said first inlet port of said manifold and having an inlet port;

means having a part extending through said case coupling said inlet port of said cryostat to said outlet port of said compressor;

a storage tank;

means including a rst pressure operated valve means having a pressure senitive element disposed in said case for coupling said outlet port of said compressor to said storage tank to admit pressure from said compressor to said storage tank when said first pressure operated valve means is opened in response to a predetermined upper limit of case pressure;

and means including a second pressure operated valve means having a pressure sensitive element disposed in said case, for coupling said storage tank to the interior volume of said case to exhaust said storage tank to said case when said second pressure operated valve means is opened in response to a predetermined lower limit of pressure in said case.

3. A cooling system comprising:

a case;

a compressor mounted in said case and having inlet and outlet ports;

a manifold having a discharge port connected to said inlet port of said compressor and having a first inlet port coupled through said case and a second inlet port opening into said case;

a cryostat externally of said case having an outlet port coupled to said first inlet port of said manifold and having an inlet port;

means having a part extending through said case coupling said inlet port of said cryostat to said outlet port of said compressor;

a storage tank;

means including a first pressure operated valve means having a pressure senstitive element disposed in said case for coupling said outlet port of said compressor to said storage tank to admit pressure from said compressor to said storage tank when said first pressure operated valve means is opened in response to a predetermined upper limit of pressure in said case;

means including a second pressure 4operated valve means having a pressure sensitive element disposed in said case for coupling said storage tank to the interior volume of said case to exhaust said storage tank to said case when said second pressure operated valve means is opened in response to a predetermined lower limit of pressure in said case;

and a pressure relief valve connected to said outlet port of said compressor and coupling said outlet port of said compressor directly to the interior volume of said case when said relief valve is open.

4. A cooling system comprising:

a case;

a compressor mounted in said case and having an inlet port and an outlet port;

a manifold having a discharge port connected to said inlet port of said compressor and having a first manifold inlet port coupled through said case and a second manifold inlet port opening into said case;

a cryostat externally of said case and having an outlet port coupled to said first manifold inlet port and having an inlet port;

means having a part extending through said case coupling said inlet port of said cryostat to said outlet port of said compressor;

a storage tank in said case;

a first electrically operated Valve coupling said outlet port of said compressor to said storage tank;

a second electrically operated valve coupling said storage tank to the interior volume of said case;

a high pressure switch disposed in said case;

an intermittent electrical device coupling said ln'ghA 13 pressure switch to said rst electrically operated valve;

and a low pressure switch disposed in said case and electrically coupled to said second electrically operated valve.

5. A cooling system comprising:

a case;

a compressor mounted in said case and having inlet and outlet ports, said inlet port communicating with the interior volume of said case;

a cryostat externally of said case having an outlet port coupled to the interior volume of said case through said case and having an inlet port;

lubricating means connected to said compressor to lubricate said compressor;

an oil separator having an inlet port connected to said outlet port of said compressor, having a gas outlet port;

uid conducting means extending through said case connecting said gas outlet port of said oil separator to said inlet port of said cryostat;

a storage tank;

means including a first pressure operated valve means having a pressure sensitive element disposed in said case, for coupling said oil and gas outlet port of said oil separator to said storage tank to discharge oil and gas therefrom to said storage tank when said first pressure operated valve means is opened in response to a predetermined upper limit of pressure in said case;

and means including a second pressure operated valve means having a pressure sensitive element disposed in said case, for coupling said storage tank to the interior volume of said case to exhaust said storage tank to said case when said second pressure operated valve means is opened in response to a predetermined lower limit of pressure in said case.

6. Apparatus as set forth in claim and in addition a pressure operated relief valve having an inlet port connected to said oil and gas outlet port of said oil separator and having an outlet port communicating with the interior volume of said case.

7. A cooling system comprising:

a case;

a compressor mounted in said case and having an inlet port and an outlet port, said inlet port communicating With the interior volume of said case;

a cryostat externally of said case and having an outlet port coupled to the interior volume of said case through said case and having an inlet port;

lubricating means connected to said compressor for lubricating said compressor;

an oil separtor having an inlet port connected to said outlet port of said compressor, having la gas outlet port and having an oil and gas outlet port;

a lter containing molecular sieve material and glass liber lilter material and having an inlet port connected to said gas outlet port of said oil separator and having an outlet port connected to said inlet port of said cryostat;

a storage tank in said case;

means including a first pressure operated valve means having a pressure sensitive element disposed in said case, for connecting said oil and gas outlet port of said oil separator to said storage tank to admit oil and gas under pressure from said oil separator to said storage tank when said rst pressure operated valve means is opened in response to a predetermined upper limit of pressure in said case;

:and means including a second pressure operated valve means having a pressure sensitive element disposed in said case for connecting said storage tank to the interior volume of said case to exhaust said storage tank to said case when said second pressure operated valve means is opened in response to a predetermined lower limit of pressure in said case;

8. A cooling system comprising:

a case;

a compressor mounted in said case and having an inlet port and an outlet port, said inlet port comunicating with the interior volume of said case;

a cryostat externally of said case and having an outlet port coupled through said case to the interior volume of said case and having an inlet port;

means having a part extending through said case coupling said inlet port of said cryostat to said outlet port of said compressor;

a storage tank in said case;

a first electrically operated valve coupling said outlet port of said compressor to said storage tank;

a second electrically operated valve coupling said storage tank to the interior volume of said case;

a high pressure switch disposed in said case and connected directly to said irst electrically operated valve to control said lirst electrically operated valve;

and a low pressure switch disposed in said case and electrically connected to said second electrically operated valve to operate said second electrically operated valve.

References Cited bythe Examiner UNITED STATES PATENTS 2,909,908 10/59 Pastuhov 62-514 3,081,935 3/63 Geisenhaver 62-470 EDWARD I. MICHAEL, Primary Examiner.

MEYER PERLIN, ROBERT A. OLEARY, Examiners, 

1. A COOLING SYSTEM COMPRISING: A CASE; A COMPRESSOR MOUNTED IN SAID CASE AND HAVING INLET AND OUTLET PORTS, SAID INLET PORT COMMUNICATING WITH THE INTERIOR VOLUME OF SAID CASE; A CRYOSTAT EXTERNALLY OF SAID CASE HAVING AN OUTLET PORT COUPLED TO THE INTERIOR VOLUME OF SAID CASE THROUGH SAID CASE AND HAVING AN INLET PORT; MEANS HAVING A PART EXTENDING THROUGH SAID CASE COUPLING SAID INLET PORT OF SAID CRYOSTAT TO SAID OUTLET PORT OF SAID COMPRESSOR; A STORAGE TANK; 